The present invention relates to indicator material particularly suited for monitoring personal exposure to hazardous materials such as hydrogen sulfide (H.sub.2 S), sulfur dioxide (SO.sub.2) and chlorine (Cl.sub.2). The indicator material is a composition comprising a pigment material, a sensitizer material and a binder component coated upon a transparent support member. Detection or monitoring is effected when the composition undergoes a visually observable reaction with the hazardous material in the atmosphere at room temperature.
Devices for monitoring exposure to hazardous material based on color change of a sensitizer are currently available. The exposure level is usually determined by comparing the color density of the exposed sensitizer with a standard final color density value. If the sensitizer is in or on an opaque or translucent medium, the color comparison is made on the side exposed to the hazardous material. If the sensitizer is on or in a transparent medium, it is then possible to make the comparison from either side. In either case, the change in color density is initially very rapid and then becomes gradual as it reaches its final density value. This final, gradual change makes it difficult to determine the exact exposure endpoint, i.e., when the sensitizer has reached its final color density value.
Prior workers have directed their attention to monitoring personal exposure to hazardous materials. See for example, Natusch, Sewell and Tanner, "Determination of H.sub.2 S in Air-An Assessment of Impregnated Paper Tape Methods," Analytical Chemistry, volume 46, page 3 (1974); Schnakenberg, "A passive Personal Sampler for Nitrogen Dioxide," Bureau of Mines Technical Progress Report 95 (1976); Ray, Carroll and Armstrong, "Evaluation of Small Color-Changing Carbon Monoxide Dosimeters," Bureau of Mines Rep. Invest. (1975); Palmer, "Personal Samplers for CO, NO and NO.sub.2 in Air," Bureau of Mines Report OFR 92-77 (1977) and Nichols, "Reactive Tapes for Automatic Environmental Analysis, Personal Vapor Monitoring Badges for Industrial Workers," National Science Foundation Report NSF/RA-780039 (1978).